1. Field of the Invention
The present invention relates to a commercial detection apparatus and commercial detection method which can effectively applied to an video recording/reproduction apparatus such as a home video tape recorder.
2. Description of the Prior Art
When reproducing a television broadcast program recorded on a video recording apparatus such as a video tape recorder, a user desires to see the television broadcast program alone, deleting commercials. Thus, it has become possible to record or reproduce a television program deleting commercials.
However, the conventional commercial detection method applied to a home video tape recorder is a simple method which cannot automatically distinguish a television main program from commercials, and the user should manually operate the video tape recorder so as to accurately delete commercials.
The conventional simple commercial detection method will be explained below with reference to an attached drawing. FIG. 1 is a block diagram showing an example of a commercial detecting circuit 20 according to the conventional commercial detecting method mounted on a video tap recorder or the like.
In FIG. 1, an RF signal inputted from an antenna 21 which is an RF input terminal is demodulated by a tuner 22, and a sound broadcasting signal is isolated from the demodulated television broadcasting signal. This sound broadcasting signal is supplied to a soundless section check circuit 23 and a sound multiplexing mode signal detecting circuit 24.
The soundless section check circuit 23 demodulates the sound broadcasting signal into a sound base band signal, whose amplitude level is used to detect soundless sections, and it is determined whether its detection time interval agrees with a predetermined rule.
Generally, a commercial interval is about 15 seconds multiplied by an integer. If the temporal interval of appearance of the soundless sections is 15 seconds multiplied by an integer, it can be determined that a reception signal is a commercial. As a soundless section may occur at other than a start and an end of a commercial, in order to prevent to erroneously identify it as a commercial when it is 15 seconds multiplied by an integer, the aforementioned interval check is carried out on the condition that soundless section of 15 seconds multiplied by an integer is repeated, for example, twice, before identifying it as a commercial and outputting a soundless section check output, i.e., a commercial detection output.
On the other hand, the sound multiplexing mode signal detection circuit 24 detects a current mode of the inputted sound broadcasting signal, i.e., monophonic, stereo, or two-language mode and encodes the current mode, for example, into a 2-bit digital data for output such as `00` for monophonic, `01` for stereo, and `10` for the two-language mode.
Moreover, a main program detecting circuit 25 includes a delay circuit 26, D flip-flop 27, and a pulse generating circuit 28. An output from the sound multiplexing signal detecting circuit 24 is supplied to the delay circuit 26 and delayed by several seconds before introduced to the input terminal of the D flip-flop.
On the other hand, this main program detecting circuit 25 supplies the pulse generating circuit 28 with the interval check output from the soundless section check circuit 23 for observing this check output for about two minutes. If no soundless section check output, i.e., if no commercial detection output is present, it is determined that the current reception signal is not a commercial but a main program and a corresponding pulse is generated. This pulse is introduced to a clock terminal of the aforementioned D flip-flop. Thus, the output of the D flip-flop always maintain an encoding value of the sound multiplexing mode of the main program.
It should be noted that the reason why the detection output of the sound multiplexing mode is delayed by the delay circuit 26 is that it is predicted that a change will occur in the sound multiplexing mode when a commercial detection which is a soundless detection is outputted, and it is necessary to prevent that the sound multiplexing mode detection output becomes unstable when the commercial detection output is supplied to the clock terminal of the D flip-flop.
Moreover, the reason why about two minutes are set for observing the commercial detection output in the soundless section check circuit 23 is that generally a commercial is completed within one minute and it is preferable to reduce the response time. An output of the aforementioned D flip-flop 27 is the output of the main program mode output circuit 25.
A mode comparator circuit 29 compares the output of the main program mode detecting circuit 25 to the output of the sound multiplexing mode signal detecting circuit 24. If they coincide, it is determined that a current reception signal is a main program; and if not, it is determined that the current reception signal is a commercial. The result of the comparison is outputted.
In general, when the sound multiplexing mode is changed from the main program mode to another mode and after the mode is not returned to the main program mode but to a third mode, it is predicted that it is a switching point of the programs. In this case, the mode comparator circuit 29 outputs a decision result that main program/commercial indefinite.
The aforementioned commercial detecting circuit 20 carries out commercial detection only according to sound information i.e., sound multiplexing mode and soundless section interval. This often causes an erroneous detection.
Especially when the main program is a stereo broadcasting or two-language broadcasting, there is no method to prevent an erroneous detection. As has been described above, it is known to detect a commercial according to sound information but it is only simplified method and there has been no definite means to enhance the detection accuracy.